Hygroscopic assisted solar photo-thermal-electric conversion system for all-day power generation and daytime water collection

•The system consists of SA hydrogel with PPy/CaCl2, TEG, hydrophilic porous PDMS.•The composite hydrogel possesses photothermal conversion and moisture absorption.•The efficient solar energy utilization and all-day power generation are achieved. In the field of solar thermal electricity, it is difficult to achieve efficient solar energy utilization during the day and continuous power supply day and night at the same time. To address this issue, an integrated system for daytime photothermal power generation combined with waste hot water evaporation and nighttime hygroscopic exothermic power generation has been designed. The system consists of multifunctional composite hydrogel, thermoelectric generator, and hydrophilic porous foam from top to bottom. Among them, the multifunctional composite hydrogel is a crosslinked sodium alginate (SA) loaded with photothermal material polypyrrole (PPy) and hygroscopic material CaCl2, and the hydrophilic porous foam is a PDMS treated by pore-making and oxygen plasma. During the night, CaCl2 and SA in the hydrogel absorb ambient moisture and then release heat, causing the temperature difference between the two sides of the thermoelectric generator to generate electricity with a power of 15.1 mW m−2. During the day, PPy in the hydrogel converts sunlight into heat for the thermoelectric generator to generate electricity with a power of 141.8 mW m−2, and the waste heat of the thermoelectric generator is then used to evaporate the water in the porous PDMS with a rate of 1.311 kg m-2h−1, realizing the multi-stage utilization of solar energy with a high efficiency of 80 %. Therefore, this integrated system can not only use solar energy efficiently, but also generate electricity continuously day and night.